For considerations relating to measuring technology and for safety reasons the potential of the electrical supply line of a radar sensor may be separated from the potential of the, often metallic, fill level container. This may for example result in a reduction in noise effects during measuring, and to a reduction in the susceptibility to interference of the measuring signals. Furthermore, such insulation may result in increased safety, for example in relation to avoiding fires that may occur as a result of a short circuit or a defect in the electrical supply line or in the electronics of the fill level radar. Thus, undesirable spark-over could, for example, lead to ignition of, or damage to, the feed material.
Furthermore, such insulation may be used for thermal separation of the feed material from the electronics, which may be necessary in particular in the case of large temperature differences between the interior of the tank and the surroundings of the tank.
WO 2005/038414 relates to a method and a device for insulating a fill level radar. To this effect the electrical insulator is arranged so as to be across an open end of a waveguide (in the following also named hollow conductor). The other end of the hollow conductor feeds the aerial. The insulator is located directly at the electronics, or it separates the hollow conductor into a lower hollow conductor and an upper hollow conductor.